An insulating glass panel or so-called thermopane has two or more glass sheets separated by annular peripheral spacers to form an insulating dead-air space. Since it is essential that the space between the glass sheets be perfectly sealed with respect to the exterior, so that dirt cannot enter this space and so that condensation cannot occur therein, extreme precautions are taken during manufacture. A sandwich is made of two or more perfectly clean and identical glass sheets flanking one or more annular spacer rings that lie somewhat inward of the aligned outer peripheries of these sheets. This is done in a controlled environment of low-humidity clean air. Then the outwardly open groove that runs around the edge of this sandwich between the sheets is filled with a viscous synthetic-resin mass that hardens, adhering to both sheets and to the spacer. Once hard this mass totally seals off the space between the sheets.
In a production-line operation this sealing of the edges is done on the panels arranged horizontally by an automatic extruding device such as described in German patent documents Nos. 2,834,902 and 2,845,475 (see also U.S. Pat. Nos. 3,974,011 and 3,947,311). This device is a pendant head which is suspended above a conveyor that can move the workpiece past underneath it. The extruder head can rotate about a vertical axis. The conveyor is provided underneath this head, which is normally set up so it can move longitudinally in the travel direction and transversely thereto, with a short transverse conveyor, with clamping devices, and with some stops. In this apparatus the stationary horizontal workpiece is sealed by running the sealing device peripherally around it, changing nozzle orientation 90.degree. and turning 90.degree. at each corner. Thus the apparatus takes up quite a bit of floorspace, and for efficiency of operation is normally set up so that while the workpiece is being sealed on one side of the apparatus the piece just sealed in the other side of the apparatus is being exchanged for a workpiece needing edge sealing.
Another system is described in German patent document No. 2,843,861 filed Oct. 1, 1980 by H. W. Beil. In this arrangement the unsealed sandwich is transported in upright position on rollers or a conveyor belt to the sealing station where suction grippers constituted as large suction cups connected to the intake of a compressor can engage against one face of it and lift it up off the conveyor. The extruder head is rotatable about a horizontal axis and is first displaced vertically to seal one vertical edge of the sandwich, after which the sandwich is pivoted 90.degree. to seal one horizontal edge. The head is pivoted through 90.degree. again and moves vertically along the next edge, whereupon it again pivots and the workpiece is moved horizontally past it to seal the last horizontal edge. Thus the vertical edges are sealed by moving the head relative to the workpiece and the horizontal edges are sealed by moving the workpiece relative to the head.
Unloading the sealed panel from such an apparatus is normally a manual operation, assisted perhaps by a small crane. In addition such an apparatus is fairly bulky, at least twice as long as the longest panel being sealed. The prior-art devices in general are wasteful of space and do not transport the heavy workpiece with the sureness and gentleness needed, especially as the freshly sealed edges of the workpiece normally are somewhat more fragile than they will be when cured somewhat.